Install rustup on windows (including ARM)

The x86 logic might be overkill since right now x86 Windows images
already have it installed, but figured might as well support it just in
case. Closes #143

action.yml

@@ -75,6 +75,16 @@ runs:
       if: runner.os != 'Windows'
       shell: bash
 
+    - run: |
+        : install rustup if needed on windows
+        if ! command -v rustup &>/dev/null; then
+          curl -LOs https://static.rust-lang.org/rustup/dist/${{ runner.arch == 'ARM64' && 'aarch64' || 'x86_64' }}-pc-windows-msvc/rustup-init.exe
+          ./rustup-init.exe -y --default-toolchain none --no-modify-path
+          echo "$USERPROFILE/.cargo/bin" >> "$GITHUB_PATH"
+        fi
+      if: runner.os == 'Windows'
+      shell: bash
+    
     - name: rustup toolchain install ${{steps.parse.outputs.toolchain}}
       run: rustup toolchain install ${{steps.parse.outputs.toolchain}}${{steps.flags.outputs.targets}}${{steps.flags.outputs.components}} --profile minimal${{steps.flags.outputs.downgrade}} --no-self-update
       shell: bash